I've been working with support. however they've gone quiet for a couple days.
I had another Iris contact sensor decide to go on strike, taking many seconds to respond. A battery pull didn't solve it. I wasn't able to reset and reconnect either, nor was I able connect the sensor as new after deleting from HE. The hub would not initialize the device as new, it would just keep causing the sensor to go into a reset loop. It connected right up to SmartThings no problem, but refused to pair with HE. I replaced it with a spare for now.
I've moved the Zigbee channel again up to 19 so I could power up SmartThings (I still have devices on it) which uses channel 15. All devices made the move again, except for arrival sensors. Very impressive agility.
I've performed a couple hub shutdowns to get the Zigbee network to heal. That has helped a bit, but I'm still seeing random lag times of 3-5 seconds on devices in the same room as the hub, I've also noticed device reports are coming in in multiples..
Temperature Report from a SmartThings Multipurpose Sensor
dev:2942019-01-04 12:29:18.204 pm infoDoor, 2nd. Floor Back Porch temperature is 45.41°F dev:2942019-01-04 12:29:11.899 pm infoDoor, 2nd. Floor Back Porch temperature is 45.41°F dev:2942019-01-04 12:29:04.845 pm infoDoor, 2nd. Floor Back Porch temperature is 45.41°F dev:2942019-01-04 12:29:01.920 pm infoDoor, 2nd. Floor Back Porch temperature is 45.41°F
Most reports come in as 2-4 events, several seconds apart. Battery pulls and reconfiguration does not help. Oddly it's only battery powered devices that are sending multiple reports.